Piston pins and like articles



y 15, 1962 H. MCKEE GAMMON ET AL 3,034,840

PISTON PINS AND LIKE ARTICLES Original Filed April 21, 1958 2Sheets-Sheet 1 A/V/VEAL INVENTOR. fiwa/"o /7 53%? 62/3/1270)? Jasgo AU/V/// I WM w M, ATTORNEYS s beans. or. sea -rs The present inventionrel-ates broadly to metal forming, and is more particularly concernedwith new and improved piston pins and like articles.

This application is a division of our copending application entitledMethod of Making Piston Pins and Like Articles, U.S Serial No. 729,885,filed April 21, 1958.

Essentially two methods have heretofore been employed in the formationof piston'pins. In one technique, a substantially cylindrical solid slugis punched from opposite ends to produce a tube having a minor amount ofresidual metal generally midway of the length of the tube. Ultimately,the residual center portion is removed by a subsequent punching orpiercing operation. An examination of the grain structure of a hollowtube or pin produced in this manner reveals lines of grain flow taperingradially outwardly in the region of the tube from which the residualmetal was removed. The immediately apparent objection to this formingmethod is the structural weakness often found in the article produced.

' Presumably in an endeavor to overcome the deficiency of the notedpunching method, metal removal by drilling techniques i often utilized.While drilling a substantially cylindrical slug along its length doesnot produce a grain flow pattern in which the lines merge generallycentrally of the slug or tube, a metallurgical examination reveals arandom grain structure along the length of the article and radiallyoutwardly into the wall thickness. I addition, the drilling procedurewastes substantial quantities of metal, and produces on the innerdiameter of the piston pin a rough or torn surface which must be removedto effect compliance with certain customer specifications.

Quite in contrast, there is produced in accordance with the teachings ofthis invention a piston pin or similar article having a grain structureimmediately distinguishable from the prior art, and in which the grainlines flow between opposite ends of the article in spaced and generallyparallel relation. This is essentially accomplished in a novel manner bya limited number of steps in which a generally cylindrical slug,preferablyhaving indented ends, is first formed or extruded into ahollow cylindrical shape having a rounded bottom, the bottom wallremoved by a piercing or similar operation, and the tubular articlefinally shaped in a Step which includes chanrfering the inner and outerdiameters thereof. Customary steps preparatory to extrusion, andincluding cleaning, etching, and lubricating, are employed as is thepractice in the art. It is accordingly a primary aim of the presentinvention to provide tubular articles having improved grain flowpatterns therein,

Another object of the invention lies in the provision of a novel pistonpin and the like having a grain flow pattern substantially continuousbetween opposite ends thereof.

Still another object of the invention is to provide a piston pinproduced from a substantially cylindrical slug which is first formedinto a generally cup-shaped cylinder, the closed end of said cylinderremoved therefrom, and the tubular member shaped to final form andessentially simultaneously beveled corners produced at opposite endsthereof along the inner and outer diameters. A further object of thepresent invention is to provide tent ice

FIGURE 2 is a sectional view through another piston pm of the prior art,and showing the grain flow pattern normally resulting from the typicaldrilling technique; FIGURE 3 is a sectional view of a piston pin of thisinvention, and showing the relatively smooth uninterrupted grain flowpattern which exists therethrough;

FIGURE 4 is a view of apparatus which may be employed to shear a slugfrom stock, and thereafter form indentations in the opposite endsthereof to facilitate subsequent processing; 7

FIGURE 5 is a view representing typical treatment steps preparatory tofurther formation of the slug;

FIGURE 6 is a View of a suitable die wherein the indented and treatedslug from FIGURES 4 and 5 may be extruded into a generally cup-shapedcylinder;

FIGURE 7 is a view of a die wherein the cup-shape may be located and thebottom wall removed therefrom;

FIGURE 8 is a view of apparatus adapted to shape the tubular articlefrom FIGURE 7 into final form, and produce beveled corners along theinner and outer diameters at opposite ends thereof; and

FIGURE 9 is a view of the same apparatus as in FIG- URE 8, and showingthe piston pin after final forming therein.

Referring now to the drawings, there is illustrated in FIGURES l and 2representative grain flow patterns generally appearing in prior artpiston pins as produced by punching and drilling techniques,respectively. Piston pin it of FIGURE 1 is typical of the articleobtained when a solid cylindrical plug is punched inwardly from oppositeends, and a tube formed having a solid center which is ultimatelyremoved by a separate operation. Adjacent the end walls of the pin it)the grain lines or bands flow generally parallel with the pin axis orcircumference, as at a and b, until generally the center section orapproximately /3 of the length of the pin is approached. In thissection, designated by the legend c, the grain flow lines or bands curveradially outwardly, and merge or even cross at times in the mannerindicated. This is indicative of the stresses to which the centerportion of the metallurgical structure is exposed as the body of themetal is moved centrally in a horizontal direction from opposite ends ofthe slug into a highly dense and compact mass in the center region ofthe tube. It is well known by those skilled in the art that a metal bodypossessing a grain structure of the character represented in FIGURE 1possesses relatively poor strength characteristics, and that fracturesoriginating in the center section c of the pin it are to be anticipatedwhen loads are placed thereon.

In an endeavor to produce satisfactory tubular articles of the pistonpin type, drilling of a solid cylindrical slug is frequently employed asa substitute method for the punching technique just described.Representative of the results obtained is the section portrayed inFIGURE 2, and it may be seen therefrom that the grain structure andother physical characteristics of the pin still leave much room forimprovement. A pin 11 drilled from one end to the other by customarytechniques frequently produces burrs and the like 12 on the innerdiameter, and this rough and torn surface must of course be removed byreaming or other procedures before a satisfactory article is obtained.In addition, it is quite apparent from FIGURE 2 that a substantialportion of the pin wall thickness possesses a random grain structure.This is represented by the legend d, and is believed to be the result ofthe radially outward compressive force exerted by the drill during itspassage from one end to the other of the pin 11. This effect is notnoticeable as the outer diameter of the pin is approached, and the grainflow pattern in this region e, is generally satisfactory. How ever, thepresence of a random grain structure in a portion of the pin wallthickness represents a source of weakness, and a danger accordinglyexists that break-down of the pin will ultimately result. And acompanion disadvantage of the drilling method is of course thesubstantial amount of metal which is wasted.

The new and improved article provided by applicants is shown in FIGURE3, and it may immediately be seen therefrom that the defects associatedwith prior art structures have been substantially entirely eliminated.Particularly, a pin 13 as formed in accordance with the teachings ofthis invention is provided with an inner diameter 14 free of burrs andthe like, and a grain structure superior to that of the cylindricaldrawn or rolled stock from which the pin 13 was formed. The grainstructure of the novel piston pin is characterized by a plurality ofconcentric lines or bands 3, generally evenly spaced and flowing fromone end of the pin 13 to the other end thereof in a substantiallystraight line path essentially parallel to the inner and outer diametersof the pin. A grain structure of this character does not present in thepin 13 a source of physical weakness, and further by practicing themethod of this invention substantial quantities of metal are saved ascontrasted with certain of the prior art forming techniques. Inaddition, since there is a complete absence of burrs thereon, no reamingstep is required.

The first step in applicants method is to sever a slug of predeterminedlength and diameter from coiled or rod stock. Piston pins arecustomarily fabricated from a carburized grade of plain or alloy steel,and among those suitable for the purpose are steels identified as SAE1016, 1022, 5015 and 8620, the Rockwell C hardness of which range up toapproximately 45.

Apparatus efi'ective to shear a slug or blank from rod stock, and toinitially form opposite ends thereof, is illustrated in FIGURE 4. Thereis provided for this purpose a shear member 15 preferably positionedadjacent a forming die 16 provided with a shaped cavity 17 receiving aslug 18 after severance from a length of rod stock by action of theshear member 15. The die 16 is provided primarily for the purpose offorming indentations in opposite ends of the slug 18, as indicated inphantom lines, to facilitate the subsequent processing of said slug. Thecavity 17 of said die includes an upwardly tapering bottom surface 19and generally parallel side walls 20 and 21 sized to accommodate withoutlooseness the slug 18. One end of the slug 18 is indented or shaped bythe bottom surface 19 of the die 16, and disposed thereabove tosimilarly indent the opposite end of said slug is a punch member 22having a tapered shaping surface 23.

A cold header die is well adapted to perform the shearing and indentingoperations, and each of these steps are accomplished with ease at roomtemperature. The provision of indented ends 24 on the slug afterprocessing through the step of FIGURE 4 is for the purpose of convenientand expeditious location of the punch member during a subsequentlyperformed extrusion step. Slippage of the punch from the slug is therebyavoided, however, indented ends 24 are not required in all instances,and accordingly, the first step may simply involve shearing from rodstock. The particular configuration of the indented ends 24 mayadditionally, of course, be varied;

however, an included angle on said ends of between and has proveneffective under most conditions encountered. Experience has furtherindicated that the surfaces forming the indented ends 24 shouldpreferably possess a flat cone angle to the center of the slug.

To assure optimum results in performance of the extrusion step, it isaccepted practice to suitably treat the slug prior to processing throughan extrusion die. The essential steps in the treatment process areidentified in FIGURE 5, and generally comprise washing, annealing,pickling and lubricating. Other steps may, of course, be interposed toobtain a particular result, and rinsing steps may, of course, berequired in the cycle shown in FIGURE 5. A convenient manner of carryingthe slugs 25 from FIGURE 4 through the steps of FIGURE 5 is in a basketor similar means 26 as shown.

The washing step is generally accomplished with hot water, and it may benecessary in certain instances that an alkali cleaning be used to removegrease and oil from the slugs. Should the alkali treatment be required,a rinse step would be called for prior to passage of the slugs into thefurnace for the annealing step. The latter step performs the importantfunction of preparing the metal for proper flow during extrusion inorder to avoid tears in the metal, and preferably the annealing step isof the spheroidizing type. A cycle found suitable in practice is to heatthe metal slug to the lower end of its critical range for between about8 and 10 hours, followed by a normal cooling for between approximately 4and 6 hours. For the purpose of removing scale and etching the surfaceof the slugs 25 prior to lubrication, a pickling step is preferablyperformed and this may be accom plished in a 10 to 12% sulphuric acidsolution. A solu tion temperature of between 140 and 160 F. performswell, and according to the degree of etching desired, the immersion timeis generally between 7 and 12 minutes.

Rinsing is then generally practiced, utilizing cold water and theoverflow technique. The slugs are then next immersed in a suitablelubricant, and phosphoric acid is a customary chemical used for thispurpose. Proprietary formulations are of course available, and thecornpound identified as Bonderlube of Parker Rustproof Company inDetroit has been found to impart the desired lubricating properties tothe slug.

The next step in the present process is to extrude the lubricated sluginto a generally cup-shaped cylindrical form 27, as shown in FIGURE 6,and this may be accomplished in a die 28 acting in combination with apunch member 29. The die 28 is provided with a straight wall 30, theinner diameter of which is greater than the outer diameter of the slug25 to permit metal flow therein upon downward movement of the punch 29.The cavity 30 is shaped at its lower end with a generally concave bottomsurface 31 against which the metal of the cold headed slug 25 is alsoforced during movement of the punch member 29 thereagainst. Roomtemperature conditions are adequate for the extrusion step, as well asthe piercing and final forming steps now to be described.

A die and punch arrangement effective to pierce or cut the cup-shapedbottom from the cylindrical form produced by the step of FIGURE 6 isshown in FIGURE 7. A suitable construction comprises a die 32 having astepped cavity 33 provided adjacent one end with a ledge surface 34supporting the marginal end portions of the cup-shaped cylinder asextruded by the preceding step. After location of said cylinder in thedie 32 in close contact with the inner diameter of the cavity 33, andagainst the ledge portion 34 of said cavity, a concaveend punch member35 is directed into the cylinder and upon reaching the lower endthereof, piercingly engages and removes the bottom or end wall 36 in themanner of FIGURE 7. Punch 35 may have a square or even convex end.

The tubular shape 37 as formed in the piercing step described isthereupon chamfered, coined and finally shaped, and this. may be donewith apparatus of the character illustrated in FIGURES 8 and 9. Suchapparatus preferably includes a die 33 having an open-ended cavity 39,shaped generally straight side walls 4% connecting with beveled cornersor coining surfaces ll, and ledge portions 42 supporting the marginalend portions of the tubular member 37 during the coining, chamfering andfinal forming steps. A punch member 43 cooperates with the die disclosedand said punch is constructed with an elongated nose portion 44 and headportion 45 provided therebetween with an angled throat portion orchamfering surface 46. To facilitate entrance into the inner diameter ofthe tube 37, the punch nose portion may be tapered as at 47. Further,the diameter of the punch head portion 45 corresponds essentially to thediameter of the cavity 39.

While the tube 37 is shown in a slightly elevated position in FIGURE 8in order to illustrate the coining surfaces 41 and ledge 4-2, it is tobe noted that the depth of the cavity 39 between the ledge portion 42and upper surface 48 of the die 33 is essentially the same as theoverall length of the tube 37 as received from the piercing step ofFZGURE 7. Further, the diameter of the cavity 39' conforms generally tothe outer diameter of the shape from FIGURE 7. Accordingly, during theforming step illustrated in FIGURES 8 and 9, the tube is not markedlychanged in length by the downward action of the punch 43; however, inthe same operation the outer diameter of the tube is increased and theinner diameter decreased. The neck or nose portion 44 of the punch 43is, to a minor degree, of lesser diameter than the inner diameter of thetube so that as said neck portion proceeds downwardly into the tube, theouter diameter of the tube is expanded outwardly to the extent permittedby the side walls it) of the cavity as and the inner diameter decreasedor contracted by radially inward metal flow to the punch 43. Statedotherwise, the neck portion 44 of the punch sizes the inner diameter ofthe tube, and in combination with the side Walls 44 of the cavity 39,also size the outer diameter of said tube to accomplish concentricity.

It is to be emphasized that prior to the present invention a seriousproblem has been presented in endeavoring to maintain the properconcentricity between the inner and outer diameters of the piston pin.This problem is essentially entirely avoided by the novel techniquesparticularly shown in FIGURES 8 and 9, and whereby in addition toestablishing concentricity between the noted pin diameters, a secondbeneficial result of restoring the inner diameter finish from thepiercing step of FIGURE 7 is obtained, essentially simultaneously.

It should be additionally noted, with respect to the sizing of the pininner and outer diameters, that when the tube 37 in FIGURE 8 is struckon one end by the punch member 43, the metal JOVES to completely fillthe annular space between said punch and the die 38. This movement,although of a relatively minor degree, insures proper coucentricitybetween the pin or tube inner and outer diameters, and at the same time,eliminates the rough surface finish on the inner diameter caused by thepiercing step of FIGURE 7. Since the metal movement of FIG- URES 8 and 9is relatively small, the essentially parallel grain flow pattern is notmaterially disturbed.

Essentially simultaneously with shaping of the openended cylinder 37 tothe final form desired, a chamfer or radius corner is placed at oppositeends of the tube on both the inner and outer diameter thereof. A chamferon the inner diameter is produced by the throat or angled surface 56 ofthe punch 43 when said punch reaches essentially the end of its stroke,and the chamfcr on the outer diameter is provided by moving saiddiameter against the sloping or coining surface 41 of the die cavity 39by action of the relatively flat bottom surface 4% of the punch headportion '45 contacting the upper surface 48 or the die 38. Thus, asingle stroke of the punch 43 finally shapes the tube and forms achamfer on the inner diameter of the tube at one end and a coinedsurface on the outer diameter at the opposite end. The tube is thenremoved from the die and located therein in an inverted position, and achamfer provided on the inner diameter adjacent the outer diameterchamfer previously provided and the outer diameter of the tube at theopposite end chamfered or coined. The tube or piston pin 13 as finallyproduced is shown in FIGURE 9, as well as FlGURE 3, and the chamferedinner diameter indicated at St and the coined outer diameter at Sll atopposite ends of the pin 13.

it may be seen from the foregoing that applicants have provided a novelmethod of forming piston pins and similar articles requiring only aminimum number of steps to produce an article having characteristics farsuperior to those found in the prior art. By use of the dieconstructions and shaping steps disclosed, the metal is moved in amanner productive of improvements in grain structure from that existingin the rod stock from which the pin is formed. There exists in the novelarticle produced by applicants a grain structure having no potentialWeakness areas therein, and the inner diameter requires no processingstep to remove burrs or the like therefrom. The method is characterizedby metal movement rather than metal removal, and in addition to theimportant advantage of a superior grain structure obtained, a greatquantity of metal is saved when contrasted with the drilling and othermethods hereinbefore described.

It is to be understood that modifications and variations may be effectedin the article disclosed without departing from the spirit of theinvention or the scope of the subjoined claims.

We claim as our invention:

1. A piston pin of substantially cylindrical tubular shape, and providedwith a cold-extruded grain structure comprising a plurality of generallyconcentric bands extending continuously from one end to the other ofsaid shape in a substantially straight line path.

2. A piston pin of substantially cylindrical tubular shape, and having acold-extruded grain structure throughout generally superior in flowpattern to that of the rod stock from which said shape was formed, andprovided with substantially concentric inner and outer diameters.

3. A piston pin of the character described, comprising an open-endedcold-extruded tubular member having smooth inner and outer diameters anda uniform wall thickness therebetween, said diameters being providedwith chamfered surfaces at opposite ends of the tubular member, and saidmember having a grain structure throughout comprising a plurality ofgenerally concentric bands extending continuously from one end to theother of said shape in a substantially straight line path.

4. A tubular article for use as a piston pin and in relatedapplications, comprising a hollow cold-extruded cylinder having aplurality of concentric evenly spaced grain lines therein extending fromone end of the cylinder to the opposite end thereof in a straight linepath substantially parallel to the inner and outer diameters of thecylinder.

5. A tubular article for use as a piston pin and in relatedapplications, comprising a cold-extruded hollow cylinder having aplurality of concentric evenly spaced grain lines therein extending fromone end of the cylinder to the op posite end thereof in a straight linepath substantially parallel to the inner and outer diameters of thecylinder, said cylinder being free of a random grain pattern in allportions thereof and having a chamfered inner diameter and coined outerdiameter at opposite ends thereof.

6. A tubular article for use as a piston pin and in relatedapplications, comprising a cold-extruded hollow cylinder having aplurality of concentric axially extending grain lines runningcontinuously and uninterruptedly between opposite ends thereof in astraight line path figuration, comprising a cold-extruded tube finallyformed With concentric inner and outer diameters by decreasingv saidinner diameter and increasing said outer diameter without changing theaxial length of said tube, said tube having a grain pattern consistingof a plurality of generally concentric bands extending continuously fromone end to the other of said tube in a substantially straight line path.

No references cited.

